Magnetic-tape apparatus comprising a threading mechanism for the displacement of a magnetic tape and a belt so as to form tape buffers

ABSTRACT

A magnetic-tape apparatus is disclosed which includes a drive mechanism for driving a magnetic tape and tape reels, a magnetic-head mechanism buffer mechanism comprising a belt (8), guide elements for guiding the belt in an operational position, a tape-threading mechanism which during the thread-out phase threads the tape out of the cassette and wraps it around the magnetic-head mechanism and during the thread-in phase threads the tape into the cassette. A belt-threading mechanism threads the belt between the guide elements into the tape path during said thread-out phase and brings the belt back into its initial position during the thread-in phase. The apparatus (1) also includes a mechanism for moving the belt-threading mechanism in such a way that the belt can be brought into the desired operational position and into said initial position.

BACKGROUND OF THE INVENTION

The invention relates to a magnetic-tape apparatus, having a frame andreel-drive means for two rotatable reels on which a magnetic tape iswound for the purpose of tape transport from one reel to the other, alength of said magnetic tape extending between the two reels. Theapparatus has at least one magnetic head for recording and/orreproducing information on/from the magnetic tape, and movabletape-threading means constructed to bring the magnetic tape, which ismovable between an initial position, in which the magnetic tape is notin contact with the magnetic-head means, and an operational position, inwhich the magnetic tape is in contact with the magnetic-head means, intosaid initial position or said operational position. Buffer means in theapparatus capable of buffering parts of the length of the magnetic tapecomprise an endless flexible belt having two guide sections whichconstitute tape guides for the magnetic tape. The magnetic tape isguided over the outer sides of the guide sections, the buffer means, insaid operational position, forms two tape buffers which in relation tothe tape transport are situated upstream and downstream of themagnetic-head means. Movable belt-threading means bring the flexiblebelt, which is movable between an initial position, in which the belt isnot in contact with the magnetic tape and is positioned at that side ofthe magnetic tape which is remote from the magnetic-head means and inwhich the belt-threading means are situated within the circumference ofthe belt, and an operational position, in which the belt is in contactwith the magnetic tape in such a way that the belt can act as a buffer,into said initial position or said operational position of the belt.Tape-drive means drive the magnetic tape past the magnetic-head means ata location in that part of the tape path which is situated between thefirst and the last tape buffer. The apparatus also has two pairs ofguide elements between which the belt is guided in its operationalposition, the two guide elements of each pair, viewed in thetape-transport direction, respectively define the beginning and the endof the guide sections of the belt in the operational position and guidethe magnetic tape in the operational position towards and away from theguide sections, the paths of movement of the tape-threading meansextending between said pairs of guide elements.

A tape-transport device for such a magnetic-tape apparatus has beenproposed in U.S. application Ser. No. 496,060, filed 3/16/90, which is acontinuation of Ser. No. 311,438 filed Feb. 15, 1989, now abandoned,which is a continuation of Ser. No. 024,731 filed Mar. 11, 1987, nowabandoned, (herewith incorporated by reference), which aims at providinga tape-transport device in which the reel movement and the movement ofthe tape past the magnetic-head means are dynamically isolated from oneanother in such a way that strongly varying speeds of the tape past themagnetic head means can be realized with a minimal delay. Thistape-transport device comprises magnetic head means and reel-drive meanscomprising two rotatable reels on which a magnetic tape is wound, whichtape, as it is unwound, is moved in its longitudinal direction away fromone of the reels with a first speed, which tape is moved passed themagnetic-head means with a second speed which is variable in magnituderelative to the first speed. The buffer means comprises an endless belt,with two tape guides which are formed by guide sections of the runningbelt and which control tape buffers disposed in the tape path betweensaid reels and the magnetic-head means. The positions of the guidesections relative to the axis of rotation of the reels and the magnetichead means can be changed in order to change the length of the tape ofthe tape buffers, which results the reel rotations being isolated fromthe movement of the tape past the magnetic-head means.

Moreover, the tape transport device proposed in said Patent Applicationenables the magnetic head and the belt to be moved between theirrespective initial positions and their operational positions with theaid of movable tape and belt-threading means. In said tape-transportdevice the belt comprises two end portions bent through 180° betweenwhich straight connecting portions are situated and in the operationalposition the belt is guided between two pairs of guide elements. In theoperational position such a belt offers resistance to the motionmovement between the guide elements because this requires some degree ofelastic deformation of the belt. Moreover, owing to its shape such abelt cannot readily be positioned between the guide elements but must beinserted between the guide elements in a specific orientation.

SUMMARY OF THE INVENTION

It is the object of the invention to construct a magnetic-tape apparatuswhose buffer system comprises a belt that offers less resistance todeformation and, consequently, offers less resistance to motion and todeformation during the displacement between the initial position and theoperational position. To this end, the invention is characterized inthat in the non-constrained situation, i.e. the situation in which thebelt is not subject to any external forces, the flexible belt has atleast substantially the shape of a circle, and the mutual arrangement ofthe guide elements and the properties of the belt are such that, if thecenter of the figure bounded by the belt circumference is situatedbetween the four guide elements, the belt is in a stable situation inwhich, as a result of the balance between the internal forces caused byelastic deformation of the belt and the forces exerted on the belt bythe guide elements, the belt adopts a shape characterized by two endportions which are bent through 180° and which adjoin two substantiallyparallel straight portions. This yields a magnetic-tape apparatus inwhich, owing to its originally circular shape, the belt offers lessresistance to motion because the elastic deformation is smaller and isthe same for every part of the belt during a revolution, enabling thebelt to be brought more simply into the operational position because theshape of the belt does not impose any preferred orientation.

A preferred embodiment of the magnetic-tape apparatus in accordance withthe invention is characterized in that in said initial position the beltis clamped between at least one stationarily arranged element and thetape-threading means and in said initial position the belt is situatedin the space between the two reels and the magnetic tape. This is anadvantage if instead of separate reels the reels are accommodated in acassette, for which it is necessary that after loading of the cassettethe belt is situated in a recess in the cassette and that the belt issituated at that side of the magnetic tape which faces the reels.

Another preferred embodiment of the magnetic-tape apparatus ischaracterized in that the guide elements are arranged stationarily andthe belt is deformed elastically as the it is brought into saidoperational position with the aid of the belt-threading means.

As a result of this the guide elements need not be movable to bring thebelt into the operational position.

A further preferred embodiment of the magnetic-tape apparatus ischaracterized in that the belt-threading means comprise a belt-threadingpin, and the path of movement of the belt-threading pin extends betweenthose two guide elements, one of each pair, which are situated at theside of the reels and between both guide elements of one of the pairs,and as the belt is brought into said operational position thebelt-threading pin brings the entire belt into one of the tape-pathbranches between the magnetic-head means and the reels, after which bytake-up onto at least one of the reels the magnetic tape is moved partlyfrom one tape-path branch into the other tape-path branch to assume itsoperational position.

As a result of this only one belt-threading pin is required for bringingthe belt into its operational position. The known tape-transport devicedoes not comprise any means with which the threading means can bedisplaced. To this end a further preferred embodiment of the magnetictape apparatus is characterized in that the belt-threading meanscomprise a belt-threading pin, in that each threading means is securedto an arm at one end of said arm, which arm near its other end issecured to a rotatable spindle having substantially the same orientationas the threading means, in that during threading-in the twotape-threading means are moved first and subsequently the belt-threadingpin, and during threading-out the belt-threading pin is moved first andsubsequently the tape-threading means, in that the movement of the armof the belt-threading pin is performed in another plane than themovement of the nearest arm of one of the tape-threading means, and inthat the arms to which the tape-threading means are secured are curvedin such a way that the movement of the arms is not restrained by thepresence of the guide elements or by the presence of the spindles towhich the arms are secured.

This results in a compact construction, which can perform the requireddisplacements for the tape and belt-threading means, which comprises asmall number of parts and in which the displacement is attended withminimal friction.

A further preferred embodiment of the magnetic-tape apparatus ischaracterized in that the arm of the belt-threading pin is arcuate, andthe arms of the tape-threading means each comprise two portions whichextend at an angle of approximately 90° relative to one another. This isnecessary in order to ensure that the movement of the threading means isnot obstructed by the drive spindle of the arm of the belt-threading pinand by the guide elements.

A further preferred embodiment of the magnetic-tape apparatus ischaracterized in that the guide elements are constructed as guiderollers, in that the tape-drive means comprise a capstan and a pressureroller, in that the belt-threading means comprise a belt-threading pin,in that the tape-threading means are constructed as tape-threadingrollers, of which at least one of the two rollers functions as apressure roller for the capstan, in that the magnetic-head meanscomprise a rotatable and a stationary magnetic-head unit, whichrotatable magnetic-head unit comprises at least one rotatable magnetichead and which stationary magnetic-head unit comprises at least onestationary magnetic head, in that the frame comprises a supporting plateformed with openings through which the tape-threading rollers can move,and in that the drive means for the reels comprise drive spindles.

This results in a construction which exhibits minimal friction betweenthe tape and the guide and tape-threading rollers during tape transport.Moreover, on account of the rotatable magnetic-head unit the apparatuscan now be constructed as a helical-scan apparatus.

Yet another preferred embodiment of the magnetic-tape apparatus ischaracterized in that the two reels are accommodated in a magnetic-tapecassette whose housing is provided with two tape guides near the frontcorners, between which tape guides a taut part of the tape extends whenthe cassette is not in operation, which housing has a recess behind saidpart of the tape, which recess has such a shape that the endless beltcan be positioned in said recess, and in that the threading means areadapted to withdraw the magnetic tape and the belt from themagnetic-tape cassette towards the magnetic-head means to bring themagnetic tape and the belt into their respective operational positions.This has the advantage that during loading of the cassette the cassettehousing can be placed with its recess over the belt, so that duringthreading-in of the magnetic tape the belt does not obstruct the tapeand during the threading-in movement towards the operational positionthe belt is readily movable into a position between the guide elements.

A further preferred embodiment of the magnetic-tape apparatus ischaracterized in that the plane of movement of the arm of thebelt-threading pin is situated above the planes of movement of the armsof the tape-threading means. This is necessary because if the plane ofmovement of the belt-threading pin should coincide with the planes ofmovement of the arms of the tape-threading means the arms would restraineach other's motions.

A further preferred embodiment of the magnetic-tape apparatus ischaracterized in that during threading-in of the belt and the magnetictape, when they are both brought from an operational position into aninitial position, after the movement of the belt-threading pin theright-hand tape-threading means begins to move first, followed by theleft-hand tape-threading means.

This has the advantage that the belt resumes the same position as in theinitial situation. As a result of this no additional operations arerequired to attain the required initial position of the belt, in which acassette can be placed over the belt.

Yet another preferred embodiment of the magnetic-tape apparatus inaccordance with the invention is characterized in that the belt is madeof polyethylene terephthalate. This material is already elasticallydeformable under a very small external force and resumes its originalshape if said external force is removed.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of a magnetic-tape apparatus in accordance with theinvention will now be described in more detail, by way of example, withreference to the drawings. In the drawings:

FIG. 1 is a cut-away plan view showing an embodiment of themagnetic-tape apparatus in the initial situation immediately afterloading of the cassette,

FIG. 2 shows a situation during threading-in of the magnetic tape,

FIG. 3 shows the situation immediately after threading-in of themagnetic tape,

FIG. 4 illustrates a situation during threading-in of the belt,

FIG. 5 shows the situation in which the belt is situated in theleft-hand tape-path branch,

FIG. 6 shows the situation in which the belt is in the operationalposition,

FIG. 7 is a graph of the magnetic-tape speed at the location of themagnetic-head means in an operational phase,

FIG. 8 illustrates a situation in which the belt is partly threaded-out,

FIG. 9 shows a situation in which the magnetic tape and the belt havebeen threaded out partly, nearly into their initial positions,

FIG. 10 illustrates the information on the magnetic tape whichcooperates with a magnetic-tape apparatus comprising rotarymagnetic-head means,

FIG. 11 illustrates the information on the magnetic tape whichcooperates with a magnetic-tape apparatus comprising rotary andstationary magnetic-head means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The magnetic-tape apparatus 1 is constructed to cooperate with amagnetic tape 7 accommodated in a cassette 29. The magnetic tape 7 iswound on reels 5, 6 accommodated in the housing of the cassette 29.After the cassette 29 has been loaded into the magnetic-tape apparatus 1the reels 5, 6 can be driven by electric motors 41, 42 by means ofspindles 3, 4 which form part of the reel-drive means. The magnetic-tapeapparatus 1 comprises magnetic-head means which in the presentembodiment comprise a rotatable magnetic-head unit, which comprises arotatable drum 9 carrying two rotatable magnetic heads 11a, and astationary magnetic-head unit 10, not shown in FIG. 1 and comprising astationary magnetic head 11b. A shutter, not shown, is arranged at thefront of the cassette 29 in its open position it exposes a length oftape 31. In the initial position of the magnetic-tape apparatus 1, inwhich the magnetic tape 7 is not in contact with the magnetic-headmeans, said length of tape 31 is stretched over two tape guides 32, 33disposed near the two front corners of the cassette 29. Behind thislength of tape 31 the cassette 29 has a recess 30 in which a flexibleendless belt 8 is situated in an initial position, which initialposition is characterized by the fact that the belt 8 is not in contactwith the magnetic tape 7. A belt-threading means constructed as abelt-threading pin 14 is arranged within the circumference of the belt8. This belt 8 is clamped between, on the one hand, four pins 28arranged on a supporting plate 2 and, on the other hand, twotape-threading means constructed as tape-threading rollers 12, 13. Inthe initial position of the belt 8 the pins 28 and the tape-threadingrollers 12, 13 are also situated in the recess 30 formed in the cassette29. The supporting plate 2 forms part of the frame of the apparatus 1.The tape-threading rollers 12, 13 and the belt-threading pin 14 aresecured to arms 15, 16, 17 connected to spindles 18, 19, 20 which, in amanner not shown, can be driven by one or more electric motors.

In the operational position of the magnetic tape 7, in which themagnetic tape 7 is in contact with the magnetic-head means (FIG. 6),buffer means are situated between the magnetic-head means and thecassette 29. The buffer means comprise the endless belt 8, which in itsoperational position, in which the belt 8 is in contact with themagnetic tape 7, is guided at its outer circumference between guideelements 21, 22, 23, 24 constructed as rollers arranged on thesupporting plate 2. These guide rollers 21, 22, 23, 24 guide themagnetic tape 7 near the entry and exit locations of the magnetic tape 7in tape buffers 34, 35 formed by the belt 8, which locations alsoconstitute the beginning and the end respectively of the guide sections36, 37 of the belt 8 which function as tape guides. The arm 17 on whichthe belt-threading pin 14 is arranged, is arcuate in order to enable therotation required for threading the belt 8 to be realised without beingobstructed by one of the guide rollers 21, 22, 23, 24. The arms 15, 16of the tape-threading rollers 12, 13 each comprise two portions whichextend at an angle of substantially 90° relative to each other in ordernot to be obstructed by the spindle 20 of the arm 17 of thebelt-threading pin 14. The arm 17 of the belt-threading pin 14 extendsabove the supporting plate 2 and the arms 15, 16 of the tape-threadingrollers 12, 13 are situated underneath the supporting plate 2. Openings25, 26 formed in the supporting plate 2 allow movement of thetape-threading rollers 12, 13 and define the paths of movement of thetape-threading rollers 12, 13.

In the operational position the magnetic tape 7 is driven by tape-drivemeans comprising a pressure-roller/capstan 27 combination driven by anelectric motor 43. Driving is effected at the location of the left-handtape-threading roller 12, which functions as the pressure roller for thecapstan 27 on the supporting plate 2. In the operational position of thebelt 8 the position of the right-hand guide section 37 is dictated byposition-detection means comprising a position-detection unit 38provided with a combination of a light source 39 and a light-sensitivecell 40. In the left-hand tape-path branch, between the tape-drive meansand the left-hand tape buffer 34, tape-tension detection means 44 arearranged. These means 44 comprise a pressure roller 46 which pressesagainst the magnetic tape 7 with a substantially constant pressure. Thetension in the magnetic tape 7 is derived from the position of thepressure roller 46.

For controlling the tape tension and the position of the belt 8 and forlocating information on the tape 7 the drive means are controlled by acontrol unit comprising a microprocessor 45. This microprocessor 45receives measurement signals (a) from the tape-tension detection means44, from the position-detection unit 38, and from the magnetic-headunits 9, 10, which together with signals (c) corresponding to thedesired situation are processed to derive control signals (b) suppliedby the microprocessor 45 for controlling the electric motors 41, 42, 43for the drive systems. The signals (c) corresponding to the desiredsituation are obtained from input means, not shown, which may beexternal to or arranged in the apparatus 1. Said input means may beconstituted by a computer.

In order to make the apparatus 1 described above suitable for thestorage of large amounts of information, in such a way that randomaccess to the information on a specific length of tape is possible, themicroprocessor 45 should be capable of performing a plurality ofadditional operations to be described hereinafter. Moreover, theinformation on the magnetic tape 7 should meet some requirements toenable the system comprising the magnetic-tape apparatus 1 and themagnetic tape 7 to be used for the above purpose. To this end theinformation on the magnetic tape 7 is divided into sections 47 (FIG. 10)having a length which is smaller than or equal to the total length ofthe tape buffered by the two tape buffers 34, 35 and constituting thebuffer capacity. In each section 47 the information is recorded inindividual discrete tracks 48. Each section 47 has a magneticallyrecorded address 49 to locate a section 47 during fast winding. Readingand writing the address 49 from/onto the magnetic tape 7 is possible bymeans of the rotary magnetic heads 11a or by means of the stationarymagnetic head 11b. In the latter case the magnetic tape 7 has a separatelongitudinal track 50 (FIG. 11).

For controlling the tape drive in order to wind the magnetic tape 7within the section 47 rapidly in either direction and hence bring theindividual discrete tracks 48 before the magnetic-head means the systemcomprises control means, which include said microprocessor 45. For therapid location of a selected address the system comprises a selectiondevice, which also includes said microprocessor 45.

The operation of the apparatus 1 described in the foregoing will now beexplained with reference to the figures. The magnetic-tape cassette 29is loaded into the apparatus 1 and brought into an initial position(FIG. 1). In this position the shutter at the front of the cassette 29is open to expose a length of tape 31 stretched between two tape guides32, 33 arranged in the front part of the cassette 29. In this positionthe two reels 5, 6 in the cassette 29, on which the magnetic tape 7 iswound, engage with drive spindles 3, 4 of the apparatus 1.

In the initial position the flexible belt 8 is situated in the recess 30in the cassette 29 behind said length of tape 31. The belt 8 is clampedbetween, on the one hand, the four pins 28 on the supporting plate 2and, on the other hand, the two tape-threading rollers 12, 13. Thebelt-threading pin 14 is situated within the periphery of the belt 8.During the tape thread-out phase the magnetic tape 7 is brought fromsaid initial position into the operational position, in which themagnetic tape 7 is in contact with the magnetic head means 9, 10 (FIG.3). The magnetic tape 7 is then withdrawn from the cassette 29 by meansof the two tape threading rollers 12, 13 and is moved between the twopairs of guide rollers 21, 22 and 23, 24 (FIG. 2) to the magnetic-headmeans 9, 10, where the magnetic tape 7 is wrapped around the drum 9through an angle of 90° (FIG. 3). The movement of the tape-threadingrollers 12, 13 is passed by rotating the spindles 18, 19 of the arms 15,16 to which the tape-threading rollers 12, 13 are secured. If theleft-hand tape-threading roller 12 had been secured to a straight armthis arm would intersect the spindle 20. In order to solve this problemthe arm 15 is constructed in such a way that it does not intersect saidspindle 20 during threading-in and threading-out of the tape 7.

Now the belt-threading phase is started, in which the belt 8 is threadedinto the tape path by means of the belt-threading pin 14. First of allthe belt 8 is threaded into the left-hand tape-path branch, which branchextends from the cassette 29 to the magnetic-head means 9, 10. This isachieved by rotating the spindle 20 of the curved arm 17 carrying thebelt-threading pin 14 in the counter-clockwise direction. Thebelt-threading pin 14 then moves the belt 8 and draws it between thosetwo guide rollers 22, 24, one of each pair, which are situated at theside of the cassette 29 and between the guide rollers 21, 22 of theleft-hand pair (FIG. 4) until the belt 8 is situated wholly within theleft-hand tape-path branch (FIG. 5). The belt-threading pin 14 thenperforms an arcuate movement through an angle of approximately 270°around the guide roller 22. Since the pivot of the arm 17 carrying thebelt-threading pin 14 is situated at the location of the spindle 20 andsince the plane in which the arm 17 moves is situated above thesupporting plate 2, which also carries the guide roller 22, the arm 17should be given an arcuate shape in order to move the belt-threading pin14 around the guide roller 22. During this phase the belt 8 is deformedelastically and the magnetic tape 7 is unwound from the left-hand reel5. Subsequently the belt-threading pin 14 is moved back until it issituated between the guide rollers 21, 22, 23, 24. Finally, in order toreach the operational position of the belt 8, the belt 8 is moved partlyout of the left-hand tape-path branch into the right-hand tape-pathbranch by winding a small length of tape onto the left-hand reel 5 (FIG.6).

In the operational situation the magnetic-tape apparatus 1 allows randomaccess to any arbitrary section of the tape 7 of a specific length bymoving the part of tape containing this section with a varying speed andin alternate directions past the magnetic-head means 9, 10, and forlocating a specific section the magnetic tape 7 can be transported witha high speed during which transport the magnetic-head means 9, 10 scanthe tape 7.

Random access is particularly suitable in the case ofhigh-information-density tape-recording, preferably helical-scanrecording, so that tape transport can be minimal and short access timescan be achieved. Moreover, in the case of helical-scan recording theinformation on the tape 7 is accommodated in the required individualdiscontinuous tracks 48 (FIGS. 10 and 11). When helical scanning is usedin the apparatus 1 in accordance with the invention this means that thetape can leave the plane of the reels 5, 6 only in the part situatedbetween the two buffers 34, 35.

Locating a specific section 47 on the tape 7 at high speed is controlledby a selection device which comprises the microprocessor 45. Dependingon the addresses 49 written by the magnetic heads 11a or 11b and thedesired address entered via the input means said microprocessor 45controls the drive of the reels 5, 6 in such a way that the tape 7 ismoved at a higher speed until the desired address is found.

As a result of this high relative tape/head speed the inclinedinformation track 48 on the magnetic tape 7 (FIG. 10) cannot be scannedcorrectly because the path of the magnetic heads 11 over the tape 7extends at a different angle when the speed of rotation of the magnetichead drum 9 is not changed. However, it is possible to read thebeginning of such an inclined track 48. This beginning should thencontain the address 49 of the section 48. Another method of reading therelevant information from the tape 7 at high tape-transport speeds is touse an additional longitudinal track 50 on the tape 7 (FIG. 11), whichis scanned by a stationary magnetic head 11b.

During this rapid-search mode the microprocessor 45 also controls theposition of the belt 8 and the tape tension. In the operational positionthe belt 8 should remain guided between the four guide rollers 21, 22 or23, 24. The position-detection unit 38 supplies information about theposition of the belt 8 to the microprocessor 45, which provides aposition correction by making the left-hand reel 5 rotate more rapidlyor slowly. If the speed with which the left-hand reel 5 takes up thetape 7 is higher or lower than the speed with which the capstan 27drives the tape 7, the tape tension in the left-hand tape-path branchwill increase or decrease respectively, causing the belt 8 to be movedto the right or the left respectively in order to restore the balancebetween the forces exerted on the belt 8 by the tape 7.

In order to control the tape tension the microprocessor 45 controls thedrive of the right-hand reel 6. If the speed with which the tape 7 isunwound from the right hand reel 6 is varied to be higher or lower thanthe speed with which the capstan 27 moves the tape 7, the tension in theright-hand tape-path branch is reduced or increased respectively. Thebalance between the forces acting on the belt 8 will cause the tapetension in the left-hand tape-path branch to change accordingly. Thecontrol system described above relates to tape transport from theright-hand reel 6 to the left-hand reel 5 but a similar line ofreasoning can be applied to tape transport in the reverse direction.

Once the desired section has been found the information within thesection can be read or random access can be applied to the informationwithin the section. Effective random access to an information carrierrequires that the relevant location on the carrier must be formedrapidly. For this purpose the tape transport past the magnetic-headmeans is controlled by control means which also include themicroprocessor 45. For locating an information track 48 within a section47 the microprocessor 45 should have information about the position ofthe track 48 within the section 47. This can be achieved by assigning aseparate track address to every track or by counting the number oftracks traversed, starting from a known position (for example the middleof the section).

Since the masses of the two reels 5, 6 are too large to realise therequired transport speeds via rotation of the reels with the aid of theelectric motors 41, 42 in the apparatus 1, another solution should beadopted. The solution to this problem is that the reels 5, 6 shouldremain stationary and that the magnetic tape 7 is moved past themagnetic-head means 9, 10 by the tape-drive means 27, tape buffers 34,35 being provided in the tape path at opposite sides of themagnetic-head means 9, 10.

In order to enable all the tracks 48 within a section 47 to be movedtowards the magnetic-head means the middle of the section 47 should besituated opposite the magnetic head 11a when the random access phasebegins, and the belt 8 should be in its centre position in which thetape lengths in the two buffers 34, 35 are equal. Moreover, the lengthof the section 47 should not be larger than the length of each tapebuffer 34, 35. In addition, the tape tension at the location of themagnetic-head means 9, 10 should be sustained during acceleration,deceleration and reversal of the direction of transport of the magnetictape 7. Said buffer system meets all the requirements. The mass of theelements to be accelerated (the mass of the length of tape plus half themass of the belt 8) is low, so that the tape-drive means 27 (thecombination of the capstan 27 and the pressure roller 12) in theapparatus 1 are capable of providing the required acceleration anddeceleration. Since the use of the belt 8 ensures that the changes inthe lengths of the portions of the tape buffers 34, 35 guided over thebelt 8 are complementary, i.e. the length reduction at one side of thebelt 8 is equal to the length increase at the other side, the tension inthe magnetic tape 7 will be maintained.

The buffer system is also very suitable for use in, for example, videorecorders in order to read the relevant information from the tape duringwinding at different speeds, for example in the "search mode" of thevideo recorder.

The reel rotation then ensures that the tape 7 at the location of theguide rollers 22, 24 nearest the cassette 29 is moved with a firstspeed. The tape-drive means 27 ensure that at the location of the guiderollers 21, 23 nearest the magnetic-head means 9, 10 and at the locationof the magnetic-head means 9, the tape 7 is moved with a second speed.The first speed of the tape 7 is also the revolution speed of the belt8. The difference between the first and the second speed of the tape 7is the translational speed of the belt 8. This translational speed isdirected perpendicularly to the connecting line between the driverollers 23, 24 of a pair and is obtained automatically without anadditional drive owing to the difference between said first and saidsecond speed. This translation enables the length of the guide sections36, 37 to be varied, which is accompanied by a change in length of thetape portions guided over the belt 8.

In this way the guide sections 36, 37 constitute tape buffers 34, 35,enabling the speed of the tape 7 past the magnetic-head means 9, 10 tobe varied considerably at a semi-stationary winding speed of the reels5, 6. This has the advantage that during fast winding the speed of thetape 7 relative to the magnetic-head means 9, 10 can be reduced forbrief periods to scan said tape with the normal speed, whereas duringthe other periods the tape 7 can be moved past the magnetic-head means9, 10 at a higher speed (FIG. 7). The position-detection element 38controls the speed of the drive spindles 5, 6 and the capstan 27 in sucha way that the belt 8 cannot exceed its permissible extreme position andin such a way that the tape tension is maintained constant.

Before the cassette 29 can be removed from the apparatus 1 the tape 7and the belt 8 should be returned into their initial positions. Thebelt-threading pin 14 is then first brought into its initial position byrotating the spindle 20 carrying the arm 17 to which the belt-threadingpin 14 is secured. The belt-threading pin 14 then withdraws the belt 8from the tape-path branches and partly returns the belt 8 to its initialposition (FIG. 8). Subsequently, the tape 7 is returned into its initialposition by moving back the two tape-threading rollers 12, 13, which iseffected by rotating the spindles 18, 19 of the arms 15, 16 carrying thetape-threading rollers 12, 13. The two tape-threading rollers 12, 13then push the belt 8 back against the four pins 28 (FIG. 9) in theapparatus 1 and the tape 7 is wound onto the reels 5, 6 by the drivespindles 3, 4. It is then necessary that the right-hand tape-threadingroller 13 is returned first, because this roller pushes the belt 8 tothe right whereas the belt 8 at the left side is retained by thebelt-threading pin 14. If the left-hand tape-threading roller 12 wouldbe returned first the belt 8 will be situated at the extreme left insidethe recess 30 in the cassette 29, because the belt 8 is not retained atthe right. Now the cassette 29 can be removed from the apparatus 1.

The threading mechanism, the buffer mechanism, the control system forthe buffer mechanism and the control system for information storage andrandom access to the information can also be employed in systems inwhich the information is recorded in one or more longitudinal tracks onthe magnetic tape. In that case the rotatable head unit may be replacedby a stationary head unit. In a system with individual discontinuoustracks the tracks may alternatively extend perpendicularly to or in thelongitudinal direction of the tape. However, the rotary head unit shouldthen be adapted accordingly.

Moreover, the stationary head unit may be provided with a plurality ofheads in the case of a plurality of address tracks. The stationary headunit may further comprise an erase head for erasing the information onthe tape. Furthermore, the rotary head unit may be provided with aplurality of heads in order to achieve an even higher informationdensity on the tape. The system is suitable both for analog and fordigital information storage.

The threading means need not necessarily be actuated by means of armswhich are rotatable about spindles. Instead, the threading means may beactuated by linkage mechanisms or slotted-link mechanisms.Alternatively, the threading means may be secured to elements which aremoved over rails or through guideways. Moreover, the belt can bethreaded by two or more threading pins, during which threading operationthe belt need not necessarily be threaded completely into one tape-pathbranch, but may be threaded into both tape-path branches at the sametime, or the guide elements can be moved outwards during threading toengage them over the belt.

The planes of movement of the arms of the belt-threading means need notnecessarily be situated above those of the arms of the tape-threadingmeans, but the two planes may also be interchanged. The supporting platewith the openings for the paths of movement of the tape-threading meansmay be dispensed with for reasons of constructional engineering. Thefour pins which are rigidly connected to the frame and against which thebelt is clamped in the initial position may be replaced by one or moreother elements such as, for example, a plate or a strip.

Instead of defining the position of the belt at one end portion it isalternatively possible to arrange detection means in the proximity ofthe permissible extreme positions of the belt end portions, whichdetection means indicate when the belt has reached one of its extremepositions. Moreover, a separate pressure roller, which presses the tapeagainst the capstan in the operational position, can be moved along withthe tape-threading means during threading of the tape instead of one ofthe tape-threading rollers being used as a pressure roller.Alternatively, the belt can be made of other materials, provided thatthese have a satisfactory elasticity, another suitable material beingfor example phosphor bronze.

We claim:
 1. A magnetic-tape apparatus (1), comprisinga frame (2),reel-drive means (3, 4) for two rotatable reels (5, 6) on which amagnetic tape (7) is wound for the purpose of tape transport from onereel to the other, a length of said magnetic tape (7) extending betweenthe two reels, magnetic-head means (9, 10) comprising at least onemagnetic head (11) for recording and/or reproducing information on/fromthe magnetic tape (7), movable tape-threading means (12, 13) constructedto bring the magnetic tape (7), which is movable between an initialposition, in which the magnetic tape (7) is not in contact with themagnetic-head means (9, 10), and an operational position, in which themagnetic tape (7) is in contact with the magnetic-head means (9, 10),into said initial position or said operational position, buffer meanscomprising an endless flexible belt (8) having two guide sections (36,37) which constitute tape guides for the magnetic tape (7), the magnetictape (7) being guided over the outer sides of said guide sections (36,37), which buffer means, in said operational position, form two tapebuffers (34, 35) which in relation to the tape transport are situatedupstream and downstream of the magnetic-head means (9, 10) and which arecapable of buffering parts of the length of the magnetic tape (7),movable belt-threading means (14) constructed to bring the flexible belt(8), which is movable between an initial position, in which the belt (8)is not in contact with the magnetic tape (7) and is positioned at thatside of the magnetic tape (7) which is remote from the magnetic-headmeans (9, 10) and in which the belt-threading means (14) are situatedwithin the circumference of the belt (8), and an operational position,in which the belt (8) is in contact with the magnetic tape (7) in such away that the belt (8) can act as a buffer, into said initial position orsaid operational position of the belt (8), tape-drive means (27) fordriving the magnetic tape (7) past the magnetic-head means (9, 10) at alocation in that part of the tape path which is situated between thefirst (35) and the last (34) tape buffer, and two pairs of guideelements (21, 22 and 23, 24) between which the belt (8) is guided in itsoperational position, the two guide elements of each pair, viewed in thetape-transport direction, respectively defining the beginning and theend of the guide sections (36, 37) of the belt (8) in the operationalposition and guiding the magnetic tape (7) in the operational positiontowards and away from the guide sections (36, 37), the paths of movementof the tape-threading means (12, 13) extending between said pairs ofguide elements (21, 22 and 23, 24),characterized in that in thenon-constrained situation, in which situation the belt (8) is notsubject to any external forces, the flexible belt (8) has at leastsubstantially the shape of a circle, and the mutual arrangement of theguide elements (21, 22, 23, 24) and the properties of the belt (8) aresuch that, if the centre of the figure bounded by the belt circumferenceis situated between the four guide elements (21, 22, 23, 24), the belt(8) is in a stable situation in which, as a result of the balancebetween the internal forces caused by elastic deformation of the belt(8) and the forces exerted on the belt (8) by the guide elements (21,22, 23, 24), the belt (8) adopts a shape characterized by two endportions which are bent through 180° and which adjoin two substantiallyparallel straight portions.
 2. A magnetic-tape apparatus (1) as claimedin claim 1, characterized in that in said initial position the belt (8)is clamped between at least one stationarily arranged element (28) andthe tape-threading means (12, 13) and in said initial position the belt(8) is situated in the space between the two reels (5, 6) and themagnetic tape (7).
 3. A magnetic-tape apparatus (1) as claimed in claim1, characterized in that the guide elements (21, 22, 23, 24) arearranged stationarily and the belt (8) is deformed elastically as it isbrought into said operational position with the aid of thebelt-threading means (14).
 4. A magnetic-tape apparatus (1) as claimedin claim 3, characterized in that the belt-threading means comprise abelt-threading pin (14), and the path of movement of the belt-threadingpin (14) extends between those two guide elements (22, 24), one of eachpair, which are situated at the side of the reels (5, 6) and betweenboth guide elements (21, 22) of one of the pairs, and as the belt (8) isbrought into said operational position the belt-threading pin (14)brings the entire belt (8) into one of the tape-path branches betweenthe magnetic-head means (9, 10) and the reels (5, 6), after which bytake-up onto at least one of the reels (5, 6) the magnetic tape (7) ismoved partly from one tape-path branch into the other tape-path branchto assume its operational position.
 5. A magnetic-tape apparatus (1) asclaimed in claim 4, characterized in thatthe belt-threading meanscomprise a belt-threading pin (14), each threading means (12, 13, 14) issecured to an arm (15, 16, 17) at one end of said arm, which arm (15,16, 17) near its other end is secured to a rotatable spindle (18, 19,20) having substantially the same orientation as the threading means(12, 13, 14), during threading-in the two tape-threading means (12, 13)are moved first and subsequently the belt-threading pin (14) and duringthreading-out the belt-threading pin (14) is moved first andsubsequently the tape-threading means (12, 13), the movement of the arm(17) of the belt-threading pin (14) is performed in another plane thanthe movement of the nearest arm (15) of one of the tape-threading means(12), and the arms (15, 16, 17) to which the tape-threading means (12,13, 14) are secured are curved in such a way that the movement of thearm (15, 16, 17) is not restrained by the presence of the guide elements(21, 22, 23, 24) or by the presence of the spindles (18, 19, 20) towhich the arms (15, 16, 17) are secured.
 6. A magnetic-tape apparatus(1) as claimed in claim 5, characterized in that the arm (17) of thebelt-threading pin (14) is arcuate, and the arms (15, 16) of thebelt-threading means (12, 13) each comprise two portions which extend atan angle of substantially 90° relative to one another.
 7. Amagnetic-tape apparatus (1) as claimed in claim 5, characterized in thatthe plane of movement of the arm (17) of the belt-threading pin (14) issituated above the planes of movement of the arms (15, 16) of thetape-threading means (12, 13).
 8. A magnetic-tape apparatus (1) asclaimed in claim 5, characterized in that during threading-in of thebelt (8) and the magnetic tape (7), when they are both brought from anoperational position into an initial position, after the movement of thebelt-threading pin (14) the right-hand tape-threading means (13) beginsto move first, followed by the left-hand tape-threading means (12).
 9. Amagnetic-tape apparatus (1) as claimed in claim 8, characterized inthatthe guide elements are constructed as guide rollers (21, 22, 23,24), the tape-drive means comprise a capstan (27) and a pressure roller(12), the belt-threading means comprise a belt-threading pin (14), thetape-threading means are constructed as tape-threading rollers (12, 13),of which at least one (12) of the two rollers functions as a pressureroller for the capstan (27), the magnetic-head means comprise arotatable (9) and a stationary (10) magnetic-head unit, which rotatablemagnetic-head unit comprises at least one rotatable magnetic head (11a)and which stationary magnetic-head unit comprises at least onestationary magnetic head (11b), the frame comprises a supporting plate(2) formed with openings (25, 26) through which the tape threadingrollers (12, 13) can move, and the drive means for the reels (5, 6)comprise drive spindles (3, 4).
 10. A magnetic-tape apparatus (1) asclaimed in claim 9, characterized in that the two reels (5, 6) areaccommodated in a magnetic-tape cassette (29) whose housing is providedwith two tape guides (32, 33) near its front corners, between which tapeguide a taut part (31) of the tape extends when the cassette (29) is notin operation, which housing has a recess (30) behind said part of thetape, which recess has such a shape that the endless belt (8) can bepositioned in said recess (30), and the threading means (12, 13, 14) areadapted to withdraw the magnetic tape (7) and the belt (8) from themagnetic-tape cassette (29) towards the magnetic-head means (9, 10) tobring the magnetic tape (7) and the belt (8) into their respectivelyoperational positions.
 11. A magnetic-tape apparatus (1) as claimed inclaim 10, characterized in that the belt (8) is made of polyethyleneterephthalate.
 12. A magnetic-tape apparatus as claimed in claim 1,characterized in that the guide elements are arranged stationarily andthe belt is deformed elastically as it is brought into said operationalposition with the aid of the belt-threading means.
 13. A magnetic-tapeapparatus as claimed in claim 2, characterized in that thebelt-threading means comprise a belt-threading pin, and the path ofmovement of the belt-threading pin extends between those two guideelements, one of each pair, which are situated at the side of the reelsand between both guide elements of one of the pairs, and as the belt isbrought into said operational position the belt-threading pin brings theentire belt into one of the tape-path branches between the magnetic-headmeans and the reels, after which by take-up onto at least one of thereels the magnetic tape is moved partly from one tape-path branch intothe other tape-path branch to assume its operational position.
 14. Amagnetic-tape apparatus as claimed in claim 1, characterized in that thebelt-threading means comprise a belt-threading pin, and the path ofmovement of the belt-threading pin extends between those two guideelements, one of each pair, which are situated at the side of the reelsand between both guide elements of one of the pairs, and as the belt isbrought into said operational position the belt-threading pin brings theentire belt into one of the tape-path branches between the magnetic-headmeans and the reels, after which by take-up onto at least one of thereels the magnetic tape is moved partly from one tape-path branch intothe other tape-path branch to assume its operational position.
 15. Amagnetic-tape apparatus as claimed in claim 1, characterized in thatthebelt-threading means comprise a belt-threading pin, each threading meansis secured to an arm at one end of said arm, which arm near its otherend is secured to a rotatable spindle having substantially the sameorientation as the threading means, during threading-in the twotape-threading means are moved first and subsequently the belt-threadingpin and during threading-out the belt-threading pin is moved first andsubsequently the tape-threading means, the movement of the arm of thebelt-threading pin is performed in another plane than the movement ofthe nearest arm of one of the tape-threading means, and the arms towhich the tape-threading means are secured are curved in such a way thatthe movement of the arm is not restrained by the presence of the guideelements or by the presence of the spindles to which the arms aresecured.
 16. A magnetic-tape apparatus as claimed in claim 1,characterized in thatthe guide elements are constructed as guiderollers, the tape-drive means comprise a capstan and a pressure roller,the belt-threading means comprise a belt-threading pin, thetape-threading means are constructed as tape-threading rollers of whichat least one of the two rollers functions as a pressure roller for thecapstan, the magnetic-head means comprise a rotatable and a stationarymagnetic-head unit, which rotatable magnetic-head unit comprise at leastone rotatable magnetic head and which stationary magnetic-head unitcomprises at least one stationary magnetic head, the frame comprises asupporting plate formed with openings through which the tape threadingrollers can move, and the drive means for the reels comprise drivespindles.
 17. A magnetic-tape apparatus as claimed in claim 1,characterized in that the two reels are accommodated in a magnetic-tapecassette whose housing is provided with two tape guides near its frontcorners, between which tape guide a taut part of the tape extends whenthe cassette is not in operation, which housing has a recess behind saidpart of the tape, which recess has such a shape that the endless beltcan be positioned in said recess, and the threading means are adapted towithdraw the magnetic tape and the belt from the magnetic-tape cassettetowards the magnetic-head means to bring the magnetic tape and the beltinto their respectively operational positions.
 18. A magnetic-tapeapparatus as claimed in claim 1, characterized in that the belt is madeof polyethylene terephthalate.